Fig. 1. A schematic diagram of the structure of the ATR, the incident angle θ is 51.6°, The refractive index of the silicon prism is 3.42

Fig. 2. Comparison of optical parameters of sea water A sample in the range of 0.2~1.0 THz
(a): Refractive index; (b): Absorption coefficient; (c): Real part of dielectric constant; (d): Imaginary part of dielectric constant

Fig. 3. Optical parameter comparison of five samples in the range of 0.2~1.0 THz for purified water, tap water, river water, seawater A and seawater B
(a): Refractive index; (b): Absorption coefficient; (c): Real part of dielectric constant; (d): Imaginary part of dielectric constant

Fig. 4. The scores of the optical parameters of purified water, tap water, river water, sea water A and sea water B in the range of 0.2~1.0 THz on the first and second principal components
(a): Score of refractive index; (b): Score of absorption coefficient; (c): Score of dielectric constant real part; (d): Score of dielectric constant imaginary part

Fig. 5. The scores of the optical parameters of purified water, tap water, river water, sea water A and sea water B in the range of 0.2~1.0 THz on the first three principal components
(a): Score of refractive index; (b): Score of absorption coefficient;(c): Score of dielectric constant real part; (d): Score of dielectric constant imaginary part

Fig. 6. Fitness curve of PSO(optimal parameter c=3.154 9, g=12.589)

Table 1. Comparison of three optimization methods of PCA-SVM combined with GA, Gridsearch and PSO